Our understanding of endocrine regulation of bone cell metabolism largely is based on studies done in vivo and on organ culture of rodent calvariae. Although organ culture permits one to separate endocrine factors in culture and to biochemically define the short-term regulatory role of each hormone, cells in organ culture do not survive beyond several days, biochemical function dramatically declines, and quantitation of cell viability and/or growth is difficult. Consequently, a suitable bone cell culture model capable of undergoing a similar level of mineralization in culture to that occurring in vivo is needed. The model not only could be used to define the biochemical roles that endocrine factors play in mineralization and bone cell metabolism, but also to screen for drugs which could be used to treat bone disease (e.g., osteoporosis). The proposed research project has three aims: 1) to examine cell culture techniques which permit neonatal, mouse calvarial cells to form three-dimensional structures and to determine which method optimizes bone cell functions (e.g., mineralization, collagen synthesis, and alkaline phosphatase activity, an osteoblastic cell marker), 2) to compare the rate of change of bone cell proliferation and function in culture for 1-3 weeks with that occurring in vivo during a comparable period, and 3) to determine if hormones and drugs associated with changes in bone metabolism in vivo exert influences on the cells in the three-dimensional cultures. The long-term objective of the study is to use the three-dimensional cultures to elucidate the role of alkaline phosphatase and endocrine factors in the mineralization process. Presently we do not know whether many hormones act on bone cells directly nor do we know the biochemical sequence of steps in biological mineralization. Although osteoporosis affects 6 million people in the U.S., the physician can only give treatments to prevent further bone resorption; no therapy to stimulate mineralization is known. Without an adequate bone model system to describe the mineralization process and to screen new drugs for their ability to induce mineralization, the problems of osteoporosis may be even greater in the future as a larger percent of the population becomes elderly.